An evaporated fuel treatment apparatus including a canister for adsorbing an evaporated fuel in a fuel tank, a control valve at a vapor path communicating with a fuel tank and a canister, has a dead-zone range where a flow of the evaporated fuel is blocked even if an opening angle of the control valve is increased in an open direction from zero opening angle, and allows the evaporated fuel to flow through over the dead-zone range. The control unit increases the opening angle from substantially zero to a predetermined angle in the dead-zone range and stands by prior to the opening control, and increases the opening angle from the predetermined angle upon the opening control. An output value by control unit set in the dead-zone range is compared with a detected value to detect a failure of the control valve.